The present invention relates to an apparatus and method for providing electrical contacts. More specifically, the present invention relates to membrane probe cards used in making a large number of electrical components.
As more and more capability is being designed into electronic components, such as microprocessors, the components are becoming increasingly complex. The more complex an electrical component becomes, the greater number of semiconductor device fabrication steps needed to form the electrical component. Semiconductor devices, such as microprocessors, are generally made from a wafer of semiconductive material. Many individual semiconductor devices are formed on a single wafer. All of the devices are made simultaneously on the wafer. Hundreds of individual semiconductor processes, which include deposition of material, ion implantation, etching, and photolithographic patterning, are conducted on a wafer to form a number of individual semiconductor devices. The wafers are sizeable. As a result, the effectiveness of each semiconductive process on each device may vary somewhat. In addition, each step or semiconductive process used to form the devices is not necessarily uniform. Generally, the semiconductive process has to perform within a desired range. The end result due to variations in the semiconductive processes as well as the variation in position is that the semiconductive devices formed may vary from one wafer to another. In addition, the semiconductive devices may vary from other semiconductive devices on the wafer.
The current practice is to test all the semiconductor devices on a wafer prior to singulation. Generally, two tests are conducted. The first test is conducted to determine if any of the individual semiconductive devices on the wafer are bad. A second test is conducted to determine a performance parameter for the good semiconductive devices on the wafer. For example, currently wafers have up to 300 microprocessors. Of course, the number of devices formed on a wafer will be higher in the future. Each of these microprocessors is tested to determine if the microprocessor is good. The speed of the microprocessor is determined in a second test. Once measured, the speed of the microprocessor is saved and the location of the microprocessor on the wafer is noted. This information is used to sort the microprocessors based on performance at the time the wafer is sliced and diced to form individual dies, each of which has a microprocessor thereon.
Each semiconductive device formed on a wafer has a number of electrical contacts. To test all the semiconductive devices on a wafer at once, many, if not all of the electrical contacts, have to be contacted. For example, testing a number of individual contacts on a wafer commonly requires upwards of 3000 different individual contacts to be made across the surface of the wafer. Testing each contact requires more than merely touching each electrical contact. An amount of force must be applied to a contact to break through any oxide layer that may have been formed on the surface of the contact. Forming 3000 contacts which are not all at the same height and not all in the same plane is also difficult. As a result, a force has to be applied to the contacts to assure good electrical contact and to compensate for the lack of planarity among the contacts.
FIG. 1 shows a membrane probe card 100 which is currently used to conduct high frequency sort and test procedures. The membrane probe card 100 includes a rigid substrate 110 and a plurality of probes 120. The probes 120 include an attached end 122 and a free end 124. The free end 124 of the probe 120 is used to contact an individual die 130. More specifically, the free end 124 of the probe 120 is used to contact individual electrical contacts 132 on the die 130. Only one die 130 is shown in FIG. 1. It should be noted that a wafer includes many dies that have not been sliced or diced into individual dies. The probe 120 includes a sharp bend 126 and also includes a more gentle bend 128. The more gentle bend 128 allows the probe 120 to act as a leaf spring. As shown in FIG. 1, the electrical contacts 132 of the die 130 have just come into contact with the individual probe 120 and specifically the free end 124 of the probe 120.
To overcome nonplanarity among the contacts 132 and to assure good electrical contact by passing through any oxidation layer on the contacts 132, the die is over driven into the rigid substrate 110. In other words, the die 130 or device under test is pressed into the probes 120 to assure that the each electrical contact 132 is contacted by a probe tip 124, and to assure that the oxidation layer has been punctured, so that good electrical contact is made. As shown by the phantom lines in FIG. 1, the device under test 130 is more closely spaced with respect to the substrate 110 so that the probes deflect and produce a larger force at the contacts 132.
The currently used membrane probe card system has a number of shortcomings. Among the shortcomings is the difficulty in controlling the amount of force produced by the probe tip. The amount of force produced at the probe tip 124 is related to the deflection of the spring shaped probe 120. If the planarity of the contacts 132 varies widely, the deflection of individual probes 120 also varies. In turn, the force at each probe tip 124 also varies widely and is difficult to control. Overdriving the probe cards not only causes variation in the force produced by the probe 120, but also causes damage to both the probe tip 124 and the product or device under test 130.
FIG. 2 shows a side view of a prior art membrane probe card 200. The membrane probe card includes a substrate 210 and a membrane 230. The membrane 230 is attached to the substrate 210. Attached to the membrane are a plurality of contacts 220. The contacts 220 are short and do not accommodate a lack of planarity. Any lack of planarity is accommodated by the membrane 230. Membrane probe card cards 200 also have shortcomings. The shortcomings include the fact that the membrane 230 may be damaged when the device under test is overdriven into the membrane probe card 200.
Thus, there is a need for a probe card which allows for force control at the probe tips so that the components of the probe card or the device under test are not damaged during testing. There is also a need for a probe card that has a more uniform or constant force at the probe tip.